I hope you didnt damage your spindle motor. For now it's difficult to find one for replacement.
At the same time, I threw away lots of garbage, including your motor which had never been used in my history.
There're 2 possibilities about your reading error.
50% possibility, the optical head died. The original model is KSS167, can be replaced by KSS221.
50% possibility, the socket of the optical head FPC(flexible print circult) contains a bad contact issue. Or the socket has a cold-joint.
Best solution is re-solder the pins of the socket, ckeck and clear the oxide on the FPC and inside of the socket.
If it doesnt work, try to replace the KSS167 then conduct a thoroughly adjustment of 5-parameter about reading ability.
Any other issues, just feel free to ask.